Device-to-device (D2D) communication is a type of radio communication in which devices communicate directly with each other, without routing data through the network infrastructure. D2D communication is currently envisioned as a way to expand the capability of existing communication networks, e.g., by providing proximity based services, public safety services, or enhanced bandwidth and/or quality services.
One way to provide enhanced bandwidth and/or quality services with D2D communication is through the use of so-called “group communication”, examples of which are disclosed in International Patent No. PCT/SE2014/050484 filed Apr. 23, 2014 and entitled “Method of Transmitting Data”. In group communication, data from a source device is transmitted to a network node by a process in which the source device shares the information with other nearby devices belonging to the group using D2D communication, and then the devices in the group concurrently transmit the shared data to the network node. In other words, the devices in the group concurrently transmit the same data to the network node, effectively increasing the overall power with which the data is transmitted.
FIG. 1 is a diagram illustrating a communication network 100 that employs group communication. As illustrated in FIG. 1, communication network 100 comprises a group 105 of devices, and a network node 110. Group 105 comprises devices A, B and C, which may be, for instance, user equipment (UE) in a Long Term Evolution (LTE) network.
The formation of group 105 typically requires some sort of user action or an automated decision procedure, which could be performed during operation of network or during initial network configuration, for example. Such action or procedure may occur at one or more of devices A, B or C, or it may occur elsewhere in communication network 100. Once a decision has been made to form group 105, one or more of devices A, B and C, or some other device, may send a request to communication network 100 for a group identifier (ID). Communication network 100 may then provide the group ID to the devices for use in group communication.
In the example shown in FIG. 1, device A uses group communication to transmit data to network node 110. In a first step shown on the left side of FIG. 1, device A transmits the data to devices B and C using D2D communication, as indicated by dotted arrows. It also sends time information that can be used by devices A, B and C to transmit the data in a synchronized manner. For instance, the time information may be a time instant when the data shall be sent by each of the devices to network node 110.
Thereafter, in a second step shown on the right side of FIG. 1, devices A, B and C transmit the data to network node 110 in the synchronized manner, as indicated by solid arrows. Typically, this means that they transmit the information at the same time, in accordance with the time information.
Network node 110 generally transmits downlink (DL) data to group 105 as if the group were a single device, e.g., a single UE. Typically, at least one device in group 105 is designated to receive the DL data and then relay the DL data to the other devices in the group via D2D communication.
The devices in group 105 share a set of group resources, which generally means that only one of the devices can transmit its own data at each time instant. Accordingly, if several devices have data to transmit, they may be required to alternate using the group resources, e.g., in a round robin fashion. The alternating use of group resources tends to delay transmissions. The negative impact of such delays, in some circumstances, may outweigh the benefits of using group communication.